Air-start systems are power sources used to provide the initial rotation to start large diesel and gas turbine engines. Air turbine starters are one example of an air-start system used on aircraft having a gas turbine engine. Gas turbine engines typically have at least one spool that includes a compressor and a turbine. When a gas turbine engine is burning fuel and operating, the spool rotates at a high speed without further assistance. However, when a gas turbine engine is initially started, the spool typically needs assistance to begin rotation. Various starters have been devised to initiate rotation of the spool.
In some gas turbine engines (for both aircraft and ground-based operations), an air turbine starter is used to start spool rotation. An air turbine starter typically includes a radial inward flow turbine, or axial flow turbine, which is connected to the high pressure compressor spool of the gas turbine engine through an accessory gearbox, in addition to various piping, valves and gears. Compressed air is blown over the turbine of the air turbine starter, which in turn causes the spool to rotate and start the gas turbine engine. Compressed air is provided to the air turbine starter by bleed air from an aircraft's auxiliary power unit (APU) or another engine on the aircraft or from an air compressor on the ground. Once the air turbine starter provides initial rotation to the high pressure compressor of the gas turbine engine, the gas turbine engine can be started and run on fuel. In addition to providing initial rotation for a gas turbine engine, air turbine starters can also be used for maintenance operations (engine washing, circulating oil during oil fill, etc.).
Gas turbine engines typically include various components, such as gears, shafts and bearings, which benefit from lubrication and cooling. An oil supply system supplies oil, or another lubricating liquid, to and from the components to lubricate and cool the components.